Skin cancer, including both melanoma and non-melanoma forms, is the most common type of cancer, with more than two million new cases expected to be diagnosed in 2010. Although a significant percentage of skin cancers are treatable, approximately 12,000 Americans will die this year due to progression of this disease. Additionally, the incidence of skin cancers has risen significantly since the 1970s, and the World Health Organization expects the skin-cancer epidemic to continue to accelerate. Due to the clear impact of skin cancer on human health, a further understanding of the genes that contribute to skin carcinogenesis is warranted. We propose to examine the mechanism by which tumor progression locus 2 (Tpl2), a serine/threonine kinase in the MAPK signal transduction cascade, affects skin cancer development by analyzing the relationship between Tpl2 and Cyclooxygenase-2 (COX- 2), an enzyme in the prostaglandin pathway implicated in skin cancer development and progression. Although mutation or overexpression of TpI2 is reported in a variety of human cancers, we have recently identified a tumor suppressor function of Tpl2 in skin cancer, with the absence of Tpl2 contributing to both tumorigenesis and inflammation. In our preliminary data we demonstrate that nearly 80% of Tpl2 knockout mice (Tpl2-/-) mice develop skin tumors compared to 16% of wild type mice. Our report is the first evidence showing a tumor suppressor function of Tpl2 in a de novo chemically induced cancer model system. Moreover, we show that Tpl2 knockout mice (Tpl2-/-) have heightened expression of cyclooxygenase-2 (COX-2), and COX-2-derived PGE2, the most abundant prostaglandin in skin. PGE2 binds to one of four G-protein linked receptors designated EP1, EP2, EP3, and EP4. Activation of two of these receptors, namely EP2 and EP4, has been shown previously to promote skin tumor development. In our preliminary data we demonstrate both in vivo and in vitro that EP2 and EP4 are elevated in Tpl2-/- mice compared to wildtype controls. However, it is unknown if the heightened COX-2 and COX-2 downstream effectors found in Tpl2-/- mice are responsible for the increase in tumor formation in Tpl2-/- mice. In this proposal we hypothesize that Tpl2-/- mice have increased inflammation and skin tumorigenesis due to a dysregulation in prostanoid signaling. In Specific Aim 1 we will determine the relationship between Tpl2 and COX-2 in carcinogenesis and inflammation. This will be performed by testing (a) if selective pharmacologic inhibition of COX-2 will decrease the susceptibility of Tpl2-/- mice to chemically-induced skin carcinogenesis and (b) if Celecoxib suppresses 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation in Tpl2-/- mice skin via the downregulation of inflammatory mediators. The in vitro experiments proposed in Specific aim 2, designed to complement the in vivo experiments proposed in Specific Aim 1, will use genetic manipulation to determine which members of the COX-2 pathway alter proliferation, migration and invasiveness of Tpl2-/- keratinocytes. Specifically, in this aim we will (a) determine the potential of the wildtype and Tpl2-/- keratinocytes to activate downstream pathways when treated with antagonists specific for EP2 and EP4 and (b) determine the proliferation, migration and invasive potential of Tpl2-/- keratinocytes transfected with MAP3K8 adenovirus and/or treated with EP antagonists. The rationale for the proposed research is that a better understanding of the regulation of molecular pathways of cancer-related inflammation may lead to further development of new strategies for cancer prevention. This work is innovative because it investigates a novel tumor suppressor function of Tpl2 and how the absence of its gene influences skin cancer development. Additionally, the proposed research will help to clarify the relationship between Tpl2 and COX-2. Identifying how Tpl2 and COX-2 interact may lead to new ways to downregulate COX-2, an enzyme often overexpressed in skin cancer, through the modulation of Tpl2. PUBLIC HEALTH RELEVANCE: Second to heart disease, cancer is the most common cause of death in both men and women in the United States. Skin cancer, including both melanoma and non-melanoma forms, is the most common type of cancer, with more than two million new cases expected to be diagnosed in 2010. Although a significant percentage of skin cancers are treatable, approximately 12,000 Americans will die this year due to progression of this disease. Additionally, the incidence of skin cancers has risen significantly since the 1970s, and the World Health Organization expects the skin-cancer epidemic to continue to accelerate. Due to the clear impact of skin cancer on human health, a further understanding of the genes that contribute to skin carcinogenesis is needed. This proposal investigates the role of one such gene, Tpl2, and how its absence contributes to skin cancer development